Typical vacuum filling devices are shown in my prior U.S. Pat. No. 2,543,788 and in the Battinich U.S. Pat. No. 2,903,023.
The filling cycle in the Battinich device includes drawing of a vacuum in the can and then admitting the filling material to the can through the same passageway to dissipate the vacuum in the can. Some of the filling material is left clinging to the filling passage side wall with the result that this material is swept out of that passageway with the violent withdrawal of air upon vacuum application to the next can to be filled. This is repeated with each can filled. In the case of a heavy product such as a puree, this amounts to as much as an ounce per can and, with a thick syrup, as much as a half ounce would be involved. This is a disadvantage when it is deemed unsanitary to return such material to the filler bowl because this requires either discharge of the filling material or its reprocessing.
The Battinich filler is not suited to filling an empty can because of the practical consideration that the vacuum available in canneries does not normally exceed 27 inches as a maximum and may be even less. Under a 27 inch vacuum, approximately a tenth of the original can air volume remains to form a large bubble in the filled can when the vacuum is dissipated. Thus, if the can is 4.5 inches high, an air bubble of 0.45 inches in height will be present whereas the can should be filled to within about 0.25 or 0.30 inches from the top.
If one attempts to modify the Battinich filling head to provide accommodation for the large air bubble, the result is to have the fill level fluctuate greatly with the not uncommon fluctuations in the vacuum applied. For example, lowering of the vacuum to 26 inches occasionally in the vacuum system is not uncommon in a system which normally operates at 27 inches, but a 26 inch vacuum would produce a bubble 0.60 inches high in a 4.5 inch can. This increase of 0.15 inches would be intolerable in a commercial can filling operation.
IN U.S. Pat. No. 2,543,788 the filling device had separate fill and vacuum passages. Some of the filling material is retained in the filling head where it would be exposed to the vacuum as it was drawn into the can.